Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.95   10.340%   $132.3528   $132.35   $132.35   $132.40  
  Purchase #2 $101.30   13.433%   $114.9076   $114.91   $114.90   $114.90  
  Purchase #3 $171.48   12.288%   $192.5515   $192.55   $192.55   $192.60  
  Purchase #4 $187.97   5.282%   $197.8986   $197.90   $197.90   $197.90  
  Purchase #5 $212.27   6.643%   $226.3711   $226.37   $226.35   $226.40  
  Purchase #6 $84.40   7.791%   $90.9756   $90.98   $91.00   $91.00  
  Purchase #7 $53.76   5.251%   $56.5829   $56.58   $56.60   $56.60  
  7 purchase totals = $931.13       $1,011.6401   $1,011.64   $1,011.65   $1,011.80